Wireless communication systems have been widely deployed in order to provide various types of communication services including voice or data. In general, a wireless communication system is a multiple access system that can support communication with multiple users by sharing available system resources (a bandwidth, transmission power, etc.). Examples of multiple access systems include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), multi carrier frequency division multiple access (MC-FDMA), etc.
Device-to-device (D2D) communication refers to a communication scheme for configuring a direct link between user equipments (UEs) and voice, data, etc. are transmitted between the UEs without passing through an evolved NodeB (eNB). D2D communication may include schemes such as UE-to-UE communication, peer-to-peer communication, etc. In addition, the D2D communication scheme can be applied to machine-to-machine (M2M) communication, machine type communication (MTC), etc.
D2D communication has been considered as one method for overcoming a burden to an eNB according to data traffic that is remarkably increased. For example, D2D communication can reduce overload of a network because data is transmitted between devices without passing through an eNB unlike in a legacy wireless communication system. In addition, according to introduction of D2D communication, effects of reduction in the number of procedures of an eNB, reduction in power consumption of devices that participate in the D2D communication, increase in data transmission speed, increase in capacity of a network, load balancing, cell coverage enlargement, etc. can be expected.